1. Field of the Invention
The invention relates to an amplifier arrangement having an inverting and a non-inverting input and an output, which arrangement comprises between a first and a second power-supply terminal:
a preamplifier comprising a first and a second transistor which are arranged as a differential pair and whose emitters are coupled to the first power-supply terminal by means of a first current source, the base of the first transistor being coupled to the inverting input and the base of the second transistor to the non-inverting input of the amplifier arrangement, which preamplifier has a first and a second output, and
an output amplifier comprising a third and a fourth transistor of opposite conductivity types, whose collector-emitter paths are arranged in series between the two power-supply terminals, a similar electrode of each transistor being coupled to the output of the amplifier arrangement, the base of the third transistor being coupled to the first output of the preamplifier and the base of the fourth transistor to the second output of the preamplifier.
Such an amplifier arrangement may be used for a variety of purposes and, in particular, in audio circuitry.
2. Description of the Related Art
Such an amplifier arrangement of a circuit design which is customary in recent amplifier circuits is disclosed in German Patent Specification No. 31 36 284. The non-inverting input of this amplifier arrangement is biassed to half the supply voltage by a voltage divider arranged between the power-supply terminals. In order to ensure that the output of the amplifier arrangement is also at half the supply voltage a negative-feedback network is arranged between the outtput and the inverting input of the amplifier arrangement. This negative-feedback network, which is often external to the integrated circuit, comprises a voltage divider using a non-integrable electrolytic capacitor. This capacitor provides full d.c. negative feedback so that the output and the inverting input are also at half the supply voltage. For the frequency spectrum of the signals to be amplified said capacitor constitutes practically a short-circuit, so that the negative-feedback network provides a signal negative feedback.
Apart from the fact that the capacitor in the negative-feedback network cannot be integrated the negative feedback has the disadvantage that the inverting input of the amplifier then becomes a low-impedance input. As a result of this, the input signal may not be applied both to the non-inverting and to the inverting amplifier in so-called bridge amplifiers to which a load is connected between the outputs of an inverting and a non-inverting amplifier arrangement. Therefore, the output signal of the non-inverting amplifier is generally applied to the inverting amplifier via a voltage divider. However, this has the disadvantage that the output signals of the inverting and the non-inverting amplifier are subjected to time delays, which may lead to distortion of the output signal of the entire amplifier.